A commonly used mechanism for loading a disc in a disc drive is that of a tray mechanism: the tray is either in an “OUT” position, in which the disc can be placed on it or taken out, or in an “IN” position, in which the disc is loaded in the drive and can be pushed out or pulled back by an electrical direct current motor. For moving the tray out or in, a voltage is applied to the motor for a specified amount of time. During this time, this voltage can have different values at different moments, first to create a smooth motion of the tray, and also because the tray motor has to control other mechanical functions of loading or unloading the disc (for example an extra force is needed when the magnetic clamper has to release the disc).
With the applied voltages, the tray must move out and in within a specified time. It is then important that the electrical and mechanical specifications of the tray mechanism are known within small tolerances and do not change during its lifetime. If the specifications do not meet the applied voltages, this would result in a too fast or too slow tray movement. In worst case situations, the tray could even not move at all, for example when the friction of the tray has increased because of contamination.